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Definition of Chemistry
Chemistry is the study of substances in
terms of:
• Composition
• Structure
• Properties
• Reactions
What is it made of?
How is it put together?
What characteristics
does it have?
How does it behave
with other substances?
Chemicals in Toothpaste
Matter
Matter
• Is what all materials are made of
• Has mass
• Occupies space
• Has characteristics called physical and
chemical properties
Physical Properties
Copper has physical properties:
•
Reddish-orange
•
Very shiny
•
Excellent conductor of heat and electricity
•
Solid at 25C
•
Melting point 1083C
•
Boiling point 2567C
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Physical properties are characteristics observed or
measured without changing the identify of a
substance: shape, physical state, odor and color.
States of Matter
All substances known as matter exist
in one of three forms or states:
• Solids
Have definite volumes and shapes
• Liquids
Have definite volumes, but take the
shapes of containers
• Gases
Have no definite volumes or shapes
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Physical Change
A physical change occurs in a substance
if there is a change in the state or in the
physical shape.
Examples of physical changes:
•Paper torn into little pieces (change of size)
•Copper hammered into thin sheets
•Water evaporating (change of state)
•Water poured into a glass (change of shape)
Chemical Properties
Chemical properties describe the ability of a
substance to interact with other substances or
to change into a new substance.
Example:
Iron has the ability to form rust
when exposed to oxygen.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Chemical Change
In a chemical change or
chemical reaction, a new
substance forms
that has
• A new composition
• New chemical properties
• New physical properties
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
**DEMO
Classify each of the following changes as
physical or chemical:
A. Bleaching a white shirt
B. Ice melting on the street
C. Toasting a marshmallow
D. Cutting a pizza
E. Iron rusting on an old car
Scientific Method
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
At a popular restaurant, where Chen is the head chef, the following occur:
•
•
•
•
•
•
Chen notices that sales of the chef’s salad have dropped.
Chen decides that the chef’s salad needs a new dressing.
In a taste test, four bowls of salad are prepared with four new dressings:
sasame seed, oil and vinegar, blue cheese and anchovies.
The tasters rate the dressing with the sesame seeds the best.
After two weeks with the new dressing, Chen notices that the orders for the
chef’s salad have doubled.
Chen decides that the sesame dressing improved the sales of the chef’s
salad because the sesame dressing improved the taste of the salad.
Chapter 2
Measurements
Measurement
You make a measurement
every time you:
• Measure your height
• Read your watch
• Take your temperature
• Weigh a cantaloupe
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Stating a Measurement
In every measurement, a number is followed by a unit.
Observe the following examples of measurements:
Number and Unit
35
m
0.25
L
225
lb
3.4
hr
Units in the Metric System
In the metric and SI systems, one unit is used for each type of
measurement:
Measurement
Length
Volume
Mass
Time
Temperature
Metric
meter (m)
liter (L)
gram (g)
second (s)
Celsius (C)
SI
meter (m)
cubic meter (m3)
kilogram (kg)
second (s)
Kelvin (K)
Scientific Notation
Scientific notation
• Is used to write very large
or very small numbers
• For the width of a human
hair of 0.000 008 m is
written as:
8 x 10-6 m
• Of a large number such as
2 500 000 s is written as:
2.5 x 106 s
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Comparing Numbers in Standard
and Scientific Notation
Here are some numbers written in standard format
and in scientific notation:
Number in
Standard Format
Scientific Notation
Diameter of Earth
12 800 000 m
1.28 x 107 m
Mass of a human
68 kg
6.8 x 101 kg
Length of a pox virus
0.000 03 cm
3 x 10-5 cm
Select the correct scientific notation for each.
A. 0.000 008
1) 8 x 106
2) 8 x 10-6
3) 0.8 x 10-5
B. 72 000
1) 7.2 x 104
2) 72 x 103
3) 7.2 x 10-4
Solution
Select the correct scientific notation for each.
A. 0.000 008
2) 8 x 10-6
B. 72 000
1) 7.2 x 104
Write each as a standard number.
A. 2.0 x 10-2
1) 200
2) 0.0020
3) 0.020
B. 1.8 x 105
1) 180 000
3) 18 000
2) 0.000 018
Solution
Write each as a standard number.
A. 2.0 x 10-2
3) 0.020
B. 1.8 x 105
1) 180 000
Reading a Meter Stick
. l2. . . . l . . . . l3 . . .
cm
• The markings on the meter stick at the end of the
blue line are read as:
The first digit
2
plus the second digit
2.7
• The last digit is obtained by estimating.
• The end of the line might be estimated between 2.7–
2.8 as half-way (0.5) or a little more (0.6), which gives
a reported length of 2.75 cm or 2.76 cm.
Known + Estimated Digits
In the length reported as 2.76 cm,
• The digits 2 and 7 are certain (known)
• The final digit 6 is estimated (uncertain)
• All three digits (2.76) are significant including the
estimated digit
Significant Figures
State the number of significant figures in each of
the following measurements:
A. 0.030 m
B. 4.050 L
C. 0.0008 g
D. 2.80 m
Solution
State the number of significant figures in each of
the following measurements:
A. 0.030 m
2
B. 4.050 L
4
C. 0.0008 g
1
D. 2.80 m
3
Rounding Off Calculated
Answers
In calculations,
• Answers must have the same
number of significant figures
as the measured numbers.
• Often, a calculator answer
must be rounded off.
• Rounding rules are used to
obtain the correct number of
significant figures.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Rounding Off Calculated
Answers
When the first digit dropped is 4 or less,
• The retained numbers remain the same.
45.832 rounded to 3 significant figures
drops the digits 32 = 45.8
When the first digit dropped is 5 or greater,
• The last retained digit is increased by 1.
2.4884 rounded to 2 significant figures
drops the digits 884 = 2.5 (increase by 0.1)
Adding Significant Zeros
• Sometimes a calculated answer requires more
significant digits. Then one or more zeros are added.
Calculated Answer
4
1.5
0.2
12
Zeros Added to
Give 3 Significant Figures
4.00
1.50
0.200
12.0
Adjust the following calculated answers to give
answers with three significant figures.
A. 824.75 cm
B. 0.112486 g
C. 8.2 L
Solution
Adjust the following calculated answers to give answers
with three significant figures.
A. 825 cm First digit dropped is greater than 5.
B. 0.112g
First digit dropped is 4.
C. 8.20 L
Significant zero is added.
Calculations with Measured
Numbers
In calculations with
measured numbers,
significant figures or
decimal places are
counted to determine
the number of figures in
the final answer.
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Multiplication and Division
When multiplying or dividing, use
• The same number of significant figures as the
measurement with the fewest significant figures.
• Rounding rules to obtain the correct number of
significant figures.
Example:
110.5
4 SF
x
0.048 = 5.304
2 SF
calculator
=
5.3 (rounded)
2 SF
Addition and Subtraction
When adding or subtracting, use
• The same number of decimal places as the
measurement with the fewest decimal places.
• Use rounding rules to adjust the number of digits in
the answer.
25.2
+ 1.34
26.54
26.5
one decimal place
two decimal places
calculated answer
answer with one decimal place
For each calculation, round the answer to give the
correct number of significant figures.
A. 2.19 x 4.2
=
1) 9
2) 9.2
B. 4.311 ÷ 0.07 =
1) 61.59
2) 62
C. 235.05 + 19.6 + 2 =
1) 257
2) 256.7
D. 58.925 - 18.2
=
1) 40.725
2) 40.73
3) 9.198
3) 60
3) 256.65
3) 40.7
Solution
A. 2.19 x 4.2
= 2) 9.2
B. 4.311 ÷ 0.07
= 3) 60
C. 235.05
+19.6
+ 2
256.65 rounds to 257
Answer (1)
D.
58.925
-18.2
40.725 rounds to 40.7
Answer (3)
*****
Exact Numbers
• Exact numbers are NOT measured and do NOT have a limited
number of significant figures. They do NOT affect the number of
sig figs in a calculated answer.
Metric and SI Prefixes
Indicate the unit that completes each of the following
equalities:
A. 1000 m = 1) 1 mm
2) 1 km
3) 1 dm
B. 0.001 g = 1) 1 mg
2) 1 kg
3) 1 dg
C. 0.1 s
1) 1 ms
2) 1 cs
3) 1 ds
1) 1 mm
2) 1 cm
3) 1 dm
=
D. 0.01 m =
Solution
Indicate the unit that completes each of the following
equalities:
A. 1000 m =
1 km
(2)
B. 0.001 g =
1 mg
(1)
C. 0.1 s =
1 ds
(3)
D. 0.01 m =
1 cm
(2)
Some Common Equalities
Conversion Factors
A conversion factor
• Is a fraction obtained from an equality
Equality: 1 in = 2.54 cm
• Is written as a ratio with a numerator and denominator
• Can be inverted to give two conversion factors for
every equality
1 in
and 2.54 cm
2.54 cm
1 in
Setting Up a Problem
How many minutes are 2.5 hours?
Given unit
=
2.5 hr
Needed unit =
? min
Unit Plan
=
hr
min
Set up problem to cancel hours (hrs).
Given
Conversion
Needed
unit
factor
unit
2.5 hr x 60 min = 150 min (2 SF)
1 hr
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
A rattlesnake is 2.44 m long. How many centimeters
long is the snake?
1) 2440 cm
2) 244 cm
3) 24.4 cm
Solution
A rattlesnake is 2.44 m long. How many
centimeters long is the snake?
2)
244 cm
2.44 m x 100 cm
1m
= 244 cm
Using Two or More Factors
• Often, two or more conversion factors are required
to obtain the unit needed for the answer.
Unit 1
Unit 2
Unit 3
• Additional conversion factors are placed in the
setup to cancel each preceding unit.
Given unit x factor 1 x factor 2 = needed unit
Unit 1
x Unit 2
x Unit 3
= Unit 3
Unit 1
Unit 2
Example: Problem Solving
How many minutes are in 1.4 days?
Given unit: 1.4 days
Factor 1
Plan:
days
Factor 2
hr
Set up problem:
1.4 days x 24 hr x 60 min
1 day
1 hr
2 SF
Exact
Exact
min
= 2.0 x 103 min
= 2 SF
If a ski pole is 3.0 feet in length, how long is the
ski pole in mm?
Solution
3.0 ft x 12 in x 2.54 cm x 10 mm =
1 ft
1 in.
1 cm
Calculator answer:
914.4 mm
Needed answer:
910 mm (2 SF rounded)
Check factor setup:
Check needed unit:
Units cancel properly
mm